Tailoring formation and proportion of strengthening phase in non-equiatomic CoCrFeNi high entropy alloy by alloying Si element. (August 2022)

• Record Type: Journal Article
• Authors: Gao, Xuefeng; Chen, Yao; Chen, Ruirun; Liu, Tong; Fang, Hongze; Qin, Gang; Su, Yanqing; Guo, Jingjie
• Is Part Of: Intermetallics. Volume 147(2022)
• Publication Date: 2022-08
• Subjects: High entropy alloy -- Microstructure evolution -- Tensile property -- Precipitated strengthening; Intermetallic compounds -- Metallography -- Periodicals; Metallic glasses -- Periodicals; Composés intermétalliques -- Métallographie -- Périodiques; 669.94
• DOI: 10.1016/j.intermet.2022.107617
• Languages: English
• ISSNs: 0966-9795

Abstract

Abstract: To adjust the formation and proportion of the strengthening phase in high entropy alloys (HEAs), the non-metallic Si element was added in non-equiatomic CoCrFeNi HEA. Co30 Cr30 (FeNi)40- x Si x HEAs ( x = 2, 4, 6, and 8 at.%, hereinafter, simplified as HSi2, HSi4, HSi6, and HSi8, respectively) were prepared. The phase evolution, tensile properties, and strengthening mechanisms were investigated. The results show that the phase structures are FCC, rich Cr–Si, and rich Ni–Si phases in HSi2 and HSi4. The rich Cr–Si phase disappears and the rich Ni–Si phase grows gradually with the increase of Si content. HSi6 presents an appropriate proportion of FCC and discontinuous rod-like rich Ni–Si phases. The mixing enthalpy ( ΔH mix ) is more suitable for the phase prediction in Co30 Cr30 (FeNi)40- x Si x HEAs. With the increase of Si content, Ni atoms diffuse into the primary rich Cr–Si phase and replace Cr atoms to form a rich Ni–Si phase. The rich Ni–Si phase has a stronger binding force due to the Ni and Si atoms with more negative ΔH mix . The yield strength gradually increases from 215 MPa to 330 MPa with the increase of Si content. HSi6 has excellent tensile strength-ductility synergy with a tensile strength of 694 MPa and a fracture strain of 67.8%, which is attributed to high strain hardening ability. The discontinuous and rich Ni–Si phase plays an important role as a strengthening phase in the deformation process, reducing the free path of dislocation movement and delaying the occurrence of necking. The FCC phase with large plastic deformation ability leads to crack passivation and maintains a certain ductility. More rich Ni–Si phases will deteriorate the ductility of HSi8. Graphical abstract: Image 1 Highlights: The non-metallic Si was alloyed to non-equiatomic Co30 Cr30 Fe20 Ni20 alloy by casting. Structure changes from FCC + Cr–Si + Ni–Si to FCC + Ni–Si phases with the increase of Si. HSi6 has excellent properties of tensile strength ∼694 MPa and fracture strain ∼67.8%. HSi6 presents appropriate proportion of FCC and discontinuous rod rich Ni–Si phases. The soft FCC and hard Ni–Si phase coordination can improve the properties of HEAs.